In dissolved air flotation clarifiers, compressed air is dissolved in a relatively solids free pressurized liquid such as previously clarified process effluent. This air charged liquid stream (called pressurized flow) is passed through a pressure reduction valve which produces a large quantity of bubbles in the liquid. The bubbles will attach to the solid particles in waste being clarified and cause such particles to float to the surface for removal. The efficiency and effluent quality of such clarifiers is dependent on control of the size and distribution of the bubbles. The performance of prior art dissolved air flotation clarifiers has been adversely affected by the presence of uncontrollable large bubbles. Such large bubbles rise very rapidly causing pockets of uncontrolled turbulence. Also, prior art clarifiers have not achieved a satisfactory degree of small bubble distribution over the entire surface of the liquid.